Polyethylene terephthalate (PET) has achieved considerable importance as a raw material for the preparation of moldings, film and fibers. Preparation of PET is described inter alia in Whinfield et al., U.S. Pat. No. 2,465,319 and in Pengilly, U.S. Pat. No. 3,047,539, and in Kirk-Othmer, Encyclopedia of Chemical Technology, Second Edition, Vol. 16, pp. 159 et. seq. (1968), all disclosures being incorporated herein by reference.
Many applications for injection and extrusion molded parts require resistance to elevated temperatures, and it is in such applications where PET manifests certain undesirable physical characteristics. Unreinforced PET has been of very limited interest for injection and extrusion molded parts due to its low HDT (Heat Deflection Temperature, also sometimes referred to as Heat Distortion Temperature). For example, PET has an HDT of about 75.degree. C. at 264 psi. HDT is a measure of an important thermal property of a thermoplastic material wherein a bar of the material, held in flexure under constant load (usually at 264 or 66 psi), deforms a specified amount and the temperature at which this specified deformation occurs is the HDT--see Billmeyer, Textbook of Polymer Science, p. 112, John Wiley and Sons, Inc. (1962).
U.S. Pat. No. 3,644,574 discloses blends of 1,4-butanediol polyesters with from about 1 to about 40 weight percent of a vinyl aromatic polymer (e.g. a styrenic polymer) which polymer may be, inter alia, a copolymer with maleic anhydride. The blends of this patent exhibit increased HDT over the unblended polyester. However, that patent discloses at column 1, lines 42-47 that the improvements observed with polybutylene terephthalate are not obtained when the polyester is poly(ethylene terephthalate).